Plants and animals are targets of many different pests, including but not limited to nematode and insect pest species. Crops are often the targets of nematode infestations. Chemical nematicides are not effective in eradicating the nematode infestations. Chemical pesticidal agents are not selective and exert their effects on non-target fauna as well, often effectively sterilizing for a period of time a field over which the chemical nematicidal agents have been applied. Some chemical pesticidal agents have been shown to accumulate in food, and to exhibit adverse effects on workers that manufacture and apply such chemical agents. Thus there has been a long felt need for methods for controlling or eradicating nematode pest infestation on or in plants, i.e., methods which are selective, environmentally inert, non-persistent, biodegradable, and that fit well into pest resistance management schemes. Plant biotechnology provides a means to control pest infestations by providing plants that express one or more pest control agents. Recombinant pest control agents have generally been reported to be proteins selectively toxic to a target pest that are expressed by the cells of a recombinant plant. Recently, small RNA molecules provided in the diet of the pest species Meloidogyne incognita have been shown to exhibit effects on the viability of the pest by affecting gene expression in the pest cells (Tobias et al. WO 01/37654 A2). Recombinant approaches to plant pest control can be selective, and are environmentally inert and non-persistent because they are fully biodegradable.
The phenomenon of dsRNA mediated gene silencing has been demonstrated in a number of plant and animal systems (Fire et al. 1998 Nature 391:806-811; Waterhouse et al. 1998 PNAS USA 95:13959-13964; Tabara et al. 1998 Science 282:430-431; Fire et al. WO 99/32619 A1; Trick et al. WO 2004/005485 A2). Methods for delivering dsRNA into the animal systems involved generating transgenic insects that express double stranded RNA molecules or injecting dsRNA solutions into the body of the animal or within the egg sac prior to or during embryonic development. Double stranded RNA mediated gene suppression has been demonstrated in plant parasitic nematodes either by providing dsRNA or miRNA's in the nematodes' diet or by soaking the nematodes in solutions containing such RNA molecules (Atkinson et al., (The University of Leeds) WO 03/052110 A2; Trick et al., (Kansas State University Research Foundation) US 2004-009876A1). Cyst nematodes (Heterodera and Globodera species) are particularly damaging pests of crop plants. Cyst nematodes include but are not limited to Heterodera avenae, H. cruciferae, H. glycines, H. hordecalis, H. latipons, H. oryzae, H. oryzicola, H. rostochinesis, H. zeae, H. schachtii, G. achilleae, G. artemisiae, G. mexicana, G. millefolii, G. pallida, G. rostochiensis, G. tabacum, G. tabacum solanacearum, G. tabacum tabacum, G. tabacum virginiae, Globodera sp. Bouro, Globodera sp. Canha, Globodera sp. Ladeiro, Globodera sp. New Zealand-EK-2004, and Globodera sp. Peru-EK-2004. These species are known to parasitize a wide variety of crops including, but not limited to barley, corn, oats, rice, rye, wheat, cabbage, cauliflower, soybean, sugar beet, spinach, mustards, and potato. Cyst nematodes are particularly problematic. Eggs persist and remain viable in the soil for many years. Genetic resistance by conventional crop breeding has limited success in identifying resistance genes effective against the wide variety of races and biotypes of the cyst nematodes. Of particular concern is the soybean cyst nematode, Heterodera glycines, herein referred to as SCN.
Therefore, there exists a need for improved methods and compositions useful to modulate gene expression by repressing, delaying or otherwise reducing gene expression within a particular plant nematode pest for the purpose of controlling the nematode infestation or to introduce novel agronomically valuable phenotypic traits.